1. Field of the Invention
The present invention relates to a battery module having end plates with increased resistance to bending.
2. Description of the Related Art
Recently, a high output rechargeable battery (“unit battery”) using nonaqueous electrolyte and having a high energy density has been developed. High capacity batteries are used as the power source for driving motors, such as those of hybrid electric vehicles.
A high capacity secondary battery (“battery module”) is composed of a plurality of unit batteries. The unit battery includes an electrode assembly having positive and negative electrodes and a separator interposed between the positive and negative electrodes, a case for receiving the electrode assembly, a cap assembly for sealing the case, and positive and negative terminals extending from the cap assembly and electrically connected to the positive and negative electrodes, respectively.
The unit batteries are arranged in series in a housing, spaced from each other by a predetermined distance, and have their terminals are connected. The unit batteries are securely fixed to each other to form a battery module.
In a conventional battery module, end plates are disposed adjacent end unit batteries of the battery module to allow a compressive force to be applied to the unit batteries, thereby fixing the unit batteries to each other. Connecting members such as restraint rods are screw-coupled to the end plates.
However, when the battery module is used for a long time, swelling occurs in the unit batteries causing the unit batteries to apply stress to the end plates. As a result, the end plates may be deformed and the connecting member may become unstably coupled from the end plates. Stress may become concentrated on the unstable coupling portion between the end plates and the connecting members, causing damage to the unstable coupling portion.
By increasing a thickness of the connecting member or the end plate, the above problem may be solved. However, a thicker connecting member results in an increase in the weight of the battery module, thus deteriorating the performance of the device powered by the battery module.